Highly effective flame retarded polystyrene by synergistic effects between expandable graphite and aluminum hypophosphite

Herein, expandable graphite (EG) and aluminum hypophosphite (AP) are used to prepare flame-retardant polystyrene (PS) composites. The flame-retardant properties of the PS composites are investigated by the limiting oxygen index (LOI) test, vertical burning test (UL-94) and cone calorimetry test (CC). With 15 wt% EG or AP incorporated alone, the PS composites show limited improvement in LOI, and fail to pass the UL-94 test. In contrast, with 10 wt% EG and 5 wt% AP added, the sample (PS/10EG/5EG) passes the UL-94 V-0 rating, and its LOI value increases from 17% to 25.5%. CC results show that the PS/10EG/5AP has a significantly depressed peak heat release rate (PHRR) by 77.7%, total heat release (THR) by 39.3%, smoke product rate (SPR) by 78.2% and total smoke product (TSP) by 82.3%. Meanwhile, the flame-retardant mechanism of the PS composites is studied by SEM, XPS, TG-IR and Py-GC/MS, and the results of which indicating a combination of condensed-phase and gaseous-phase activity during combustion. •Combination with EG and AP greatly enhances the flame retardance of polystyrene.•Synergistic efficiency (SE) is calculated and discussed for different PS/EG/AP composites.•EG/AP plays a flame-retardant role in both condensed and gaseous phases during combustion.